Tutorials covering programming languages, type systems, architecture, tooling, and the patterns used to build software that lasts. Each chapter is standalone, built around real examples and verified facts.
A generator is a function that produces a sequence of values lazily. Instead of building a list and returning it, the function yields values one at a time, and the consumer receives them as they are produced. Dart has two kinds of generators: synchronous generators marked with sync*, which return an Iterable, and asynchronous generators…
A Compose service is an abstract definition of a container. When the service is started, Compose creates one container for it. The scale option and the –scale flag create multiple containers for the same service, and Docker’s embedded DNS server load-balances the requests across them. The scaling is horizontal: more containers of the same service,…
async and await are the syntax sugar on top of Promises that makes asynchronous code read like synchronous code. Instead of chaining .then() calls, you write await in front of a Promise — and the function pauses until the Promise settles, without blocking the rest of the program. Key point: async marks a function as…
MongoDB stores documents, and Node.js works with objects. The two are close cousins: a MongoDB document is a BSON object, and a Node.js application is full of JavaScript objects. But the similarity is deceptive. MongoDB accepts any valid BSON document, so a collection can contain documents with different fields, different types, and different structures. For…
useRef returns a plain object with a single property, current. React creates that object once, on the first render, and returns the same object on every subsequent render. Nothing about the object is special. It is not a proxy, it is not reactive, and it is not tracked by the reconciler. It is a box….
The previous chapter introduced lifetimes as the compiler’s mechanism for preventing dangling references. This chapter is about the syntax and the patterns. The ‘a annotation is not a runtime value and it is not a memory address. It is a name for a region of code, and the compiler uses it to reason about how…
A query that contains another query inside it. This is the essential idea behind the subquery, and it is one of the most powerful tools in SQL. A subquery lets you use the result of one query as input to another, without creating temporary tables or writing procedural code. The WHERE clause is the most…
Utility-first CSS has a well-known friction point. When the same set of utilities appears on every instance of a component — a button, a card, a badge — the markup is repeated, and a change to the pattern requires editing every occurrence. The @apply directive is Tailwind’s answer. It takes a list of utility classes…
Some data has no natural bottom. A JSON value contains arrays and objects, which contain more JSON values, which contain more arrays and objects. A file tree contains directories, which contain files and more directories. A linked list node points to the next node, which points to the next, until one points to nothing. These…
A component that loads data asynchronously has three states: loading, loaded, and failed. The traditional way to handle these is a v-if chain: show a spinner while loading is true, show the content when data is present, and show an error when error is set. Every component repeats this pattern, and every parent repeats the…